Light gathering apparatus

ABSTRACT

A light gathering apparatus for gathering luminous fluxes incident from two different directions, including a luminous flux gathering optical element which includes an array of continuous first and second emission surfaces alternately and symmetrically arranged with respect to bisectors of the angle defined by and between the luminous fluxes.

This application is a division of application No. 08/047,400, filed Apr.19, 1993, now abandoned, which is a division of application No.07/679,271, filed Apr. 2, 1991, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for gathering light fluxesincident from different directions to emit light flux in a predeterminedsingle direction, and more particularly relates to a gathering apparatuswhich gathers and emits light fluxes of the same polarization.

2. Description of Related Art

A known light gathering apparatus for collecting light fluxes incidentfrom different directions, as shown in FIG. 10 includes a polarizationbeam splitter 12 which splits a light flux which is emitted from a lightsource 10 and collimated by a collimating lens 11 into two linearpolarization components. Wedge-shaped prism 20 which gathers the splitbeams without regard to their polarization.

Among the light fluxes incident upon the polarization beam splitter 12is a P-polarized beam component which has an oscillation direction ofelectromagnetic vector parallel to the plane of the drawing. It istransmitted through a connecting surface 12a of the polarization beamsplitter 12 and transmitted through a λ/2 plate 13 where the oscillationdirection is converted to be perpendicular to the plane of the drawing(shown as two-dotted and dashed lines in FIG. 10). The light is thenreflected by a mirror 14 to be incident upon the first face 21 of thewedge-shaped prism 20.

On the other hand, an S-polarized beam component which has anoscillation direction perpendicular to the plane of the drawing isreflected by the connecting surface 12a of the polarization beamsplitter 12 and is made incident upon a second face 22 of thewedge-shaped prism 20 (shown as dotted and dashed lines).

The light fluxes are refracted upon incidence of the wedge-shaped prism20 at the first face 21 and the second face 22 thereof, and then totallyreflected by the internal surfaces of the first and second faces 21 and22, respectively. The reflected light fluxes are emitted from a thirdface 23 of the wedge-shaped prism 20.

In the conventional arrangement shown in FIG. 10, only linearlypolarized light of predetermined direction is selectively collected fromall of the polarizations existing in natural light and is emitted.

In the known light gathering apparatus as shown in FIG. 10, the gatheredlight fluxes of two different directions are emitted from the sameoutgoing surface (third face) 23 of the wedge-shaped prism 20, but thereis a difference in the emission angle between the outgoing lights fromthe third face 23. This results in an increase of irregularity ofluminance, depending upon the distance of the object to be illuminatedfrom the outgoing face 23. Furthermore, in the known light gatheringapparatus mentioned above, it is necessary to use a projection lenswhich has a small F-number, i.e., a projection lens of a large diameterin order to decrease the loss of quantity of light. However, generallyspeaking, it is very difficult to realize such a projection lens.

SUMMARY OF THE INVENTION

The primary objective of the present invention is to provide a lightgathering apparatus which will emit a substantial portion of thegathered light in the same direction.

To achieve the objective mentioned above, according to the presentinvention, there is provided a light gathering apparatus for gatheringluminous fluxes incident from two different directions. The apparatuscomprises a luminous flux gathering optical element including an arrayof continuous first and second reflection or emission surfaces which arealternately and symmetrically arranged with respect to bisectors of anangle defined by and between the luminous fluxes.

In an embodiment of the present invention, the luminous flux gatheringoptical element is realized by a mirror including an array of continuousfirst and second reflection surfaces which are alternately arranged toreflect the multifariously incident luminous fluxes in the samedirection.

In another embodiment of the present invention, the luminous fluxgathering optical element is realized by a composite prism having a flatincident surface on which the luminous fluxes are made incident from thedifferent directions, and an array of continuous first and secondemission surfaces which are alternately arranged to refract the incidentluminous fluxes in the same direction.

The present disclosure relates to subject matter contained in Japanesepatent application No. 02-91233 (filed on Apr. 5, 1990) which isexpressly incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below in detail with referenceto the accompanying drawings, in which;

FIG. 1 is a schematic diagram showing the optical path of a lightgathering apparatus according to a first embodiment of the presentinvention;

FIG. 2 is a diagram showing the optical path of a light gathering mirrorshown in FIG. 1;

FIGS. 3 and 4 are diagrams of optical paths of light gathering mirror,which have different apex angles;

FIG. 5 is a schematic diagram showing an optical path of a lightgathering apparatus according to a second embodiment of the presentinvention;

FIGS. 6 through 8 are explanatory views of operations of the lightgathering prism shown in FIG. 5;

FIG. 9 is a schematic diagram showing an optical path of a lightgathering apparatus according to a third embodiment of the presentinvention; and,

FIG. 10 is a schematic diagram showing an optical path of a known lightgathering apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 through 4 show a first embodiment of the present invention, inwhich a light gathering apparatus is comprised of a light gatheringmirror 30 having a plurality of mirror elements 30a made of continuoustriangular posts with apex angles of 120 degrees.

FIG. 1 shows a light source apparatus using the light gathering mirror30 (light gathering apparatus) by way of example. The light sourceapparatus includes a light source 10, a collimating lens 11, apolarization beam splitter 12, aλ/2 plate 13, two mirrors 14 and 15, anda light gathering mirror 30. A light flux diffused from the light source10, including all polarizations, is collimated by the collimating lens11 and is then split by the polarization beam splitter 12 into aP-polarized wave component and an S-polarized wave component. TheP-polarized wave component transmitted through the polarization beamsplitter 12 is made incident upon the light gathering mirror 30 throughthe λ/2 plate 13 (shown as two-dotted and dashed lines in FIG. 1). Onthe other hand, the S-polarized wave component which is reflected by theconnecting surface 12a of the polarization beam splitter 12 is madeincident upon the light gathering mirror 30 from a direction opposite tothat of the P-polarized wave component through the mirrors 14 and 15(shown as dotted and dashed lines).

The apex angle of the reflection surfaces R1 and R2 of each mirrorelement 30a (triangular post) of the light gathering mirror 30 is 120degrees. The bisectors of the apex angles of the mirror elements 30amust be parallel to each other and perpendicular to the referencesurface S (see FIG. 2). In the illustrated embodiment, the reflectionsurfaces R1 and R2 have the same length and accordingly the inclinationangles of the reflection surfaces R1 and R2 are 30 degrees with respectto the reference surface S. However, the reflection surfaces R1 and R2may vary in length, resulting in a jagged array of peaks (triangularposts). The light flux A (corresponding to the P-polarized wavecomponent, transmitted through the polarization beam splitter 12), andthe light flux B (corresponding to the S-polarized wave component,reflected by the connecting surface 12a of the polarization beamsplitter 12), and the mirrors 14 and 15 are made symmetrically incidentupon the mirror elements 30a from the opposite sides at an incidentangle of 60 degrees with respect to lines N normal to the referencesurface S of the light gathering mirror 30. Thus, according to thepresent invention, all of the light fluxes (i.e., the light fluxes A andB incident upon the light gathering mirror 30) are reflected by thelight gathering mirror 30 in a direction perpendicular to the referencesurface S.

FIG. 2 shows an enlarged view of the reflection surfaces R1 and R2 ofthe mirror elements 30a of the light gathering mirror 30. The light fluxA from one side is totally reflected by all the reflection surfaces R1,as shown by solid lines, so that a parallel light flux perpendicular tothe reference surface S is obtained. On the other hand, the light flux Bfrom the other side is totally reflected by all the reflection surfacesR2, as shown by imaginary lines, so that a parallel light fluxperpendicular to the reference surface S is obtained.

The reflected parallel light flux includes, in equal proportions, thecomponent from the reflection surfaces R1 and the component from thereflection surfaces R2. In FIG. 2, the reflected lights of the fluxes Aand B are designated by numerals 1, 2, 3 and 4 to show the collection ofthe lights. As can be seen from FIG. 2, there is no substantialirregularity of illumination light (luminance) and the reflected lightshave the same direction.

Supposing that the light fluxes A and B are both defined by a circle ofa diameter a, the resultant light flux reflected by the light gatheringmirror 30 is in the shape of an ellipse having a major diameter of 2aand a minor diameter of a. Such an elliptical light flux can be shapedinto a circular light flux, if necessary. Or, the elliptical light fluxcan be advantageously used for a rectangular image forming system.Namely, since an image plane is usually rectangular, such as atelevision or a photographic film or the like, such a rectangular imageplane can be effectively illuminated with the elliptical light flux.

The optimum apex angle of the mirror element 30a defined by the adjacentreflection surfaces R1 and R2 is 120 degrees, as mentioned above toensure a uniform luminance and the same emission direction of theillumination light flux. Namely, the optimum apex angle of the mirrorelement 30a defined by the adjacent reflection surfaces R1 and R2 is 120degrees.

If the apex angle θ of the mirror element 30a (the triangular post) issmaller than 120 degrees, the reflection surfaces R1 and R2 can not bewholly used as reflection surfaces when the light fluxes A and B aremade incident upon the reflection surfaces R1 and R2 from the oppositedirections so as to obtain a resultant parallel light flux reflectedfrom the light gathering mirror 30 in the same direction, as shown inFIG. 3. In other words, only parts of the respective reflection surfacesR1 and R2 can be used to obtain a parallel light flux emitted from thelight gathering mirror 30 in the same direction. Consequently, there areareas in which no light flux exists, resulting in an increasedirregularity of luminance on the object (not shown) to be illuminated.The irregularity can be reduced, to some extent, by making the lightfluxes A and B incident upon the respective reflection surfaces R1 andR2 primarily parallel to the associated reflection surfaces R1 and R2,if it is permissible that the emission direction of the light fluxreflected by the reflection surfaces R1 is slightly different from thatof the light flux reflected by the reflection surfaces R2.

Conversely, if the apex angle θ is larger than 120 degrees, althoughthere is little or no irregularity of luminance, a part of the lightflux which is to be reflected by the reflection surfaces R1 is reflectedby the reflection surfaces R2 and deviates from the optical path, as canbe seen in FIG. 4. This increases the loss in the quantity of light.

FIGS. 5 through 8 show a second embodiment of the present invention.

In this embodiment a composite prism 40 is used instead of the lightgathering mirror 30 as in the first embodiment. The light fluxes of thesame polarization direction incident from two different directions areemitted from the composite prism 40 in the same direction by refractionrather than reflection. The composite prism 40 has a flat incidentsurface 40a (reference surface S) and a serrated outgoing surface(emission surface) 40b in cross section, made of continuous triangularposts. The light fluxes from two different directions are madesymmetrically incident (having the same angle of incidence) upon thesurface 40a of the composite prism 40 but in different directions withrespect to the bisectors N of the apexes of the triangular posts 40b.The remaining construction is the same as that of the first embodimentshown in FIG. 1.

FIG. 6 shows the principle of refraction of a light flux at a boundarysurface between two media having different refractive indexes.

Supposing that the refractive indexes of a first medium on the incidentside and a second medium on the emission side are n₁ and n₂,respectively, we have the following equation:

    n.sub.1 ·sin θ1=n.sub.2 ·sin θ2(1)

wherein θ 1 is the incident angle, and θ 2 is the angle of refraction.

When it is supposed that the diameters of the incident luminous flux(light flux) and the outgoing luminous flux are φ 1 and φ 2,respectively, a magnification m of a change in diameter of the luminousflux by refraction is obtained by: ##EQU1##

To satisfy m<1, the value of n₁ must be larger than the value of n₂.That is, n₁ >n₂.

FIG. 7 shows a refraction at the boundary surfaces O of the triangularposts 40b. In FIG. 7, the apex angle of the triangular posts 40b is 2 α,and the surface perpendicular to the bisector of the apex angleconstitutes the reference surface S, similarly to the first embodiment.

To eliminate the vignetting of the light flux, the incident angle θ 1and the angle θ 2 of refraction at the boundary surface O must satisfythe following formulae, respectively.

    θ1=90-2α,θ2=90-α

Then, the equation (1) mentioned above can be replaced with thefollowing equation:

    n.sub.1 ·cos 2α=n.sub.2 ·cos α

From this equation, we have:

    cos α={1+ 1+8(n.sub.1 /n.sub.2).sup.2 !.sup.1/2 }/{4·n.sub.1 /n.sub.2 }                                                (3)

And;

    m=cos θ2/cos θ1=sin α/sin 2α=1/(2 cos α)(4)

The operation of the composite prism 40 is as follows (FIG. 8).

At the boundary surface 40a (reference surface S) of the incident side,the following formula is satisfied;

    n.sub.0 ·sin α.sub.0 =n.sub.1 ·sin α(5)

From the equations (2) and (4), the resultant magnification m' is givenby;

    m'={cos α/cos α.sub.0 }·{1/2cos α}=1/2cos α.sub.0                                             (6)

Thus, if the refractive indexes of three kinds of media are determined,the apex angle α, to prevent the occurrence of the vignetting, can bedetermined in accordance with the equation (3), whereby the incidentangle α0 can be obtained by the equation (5).

Having obtained the value of α₀, the resultant magnification m' can bedetermined by equation (6).

For example, when the composite prism 40, made of Bk7 (n₁ =1.51633) isdisposed in the air (n₀ =n₂ =1);

α=27.008°

α₀ =43.518°

m'=0.690

When these requirements are satisfied, the light fluxes A and B from thedifferent directions can be gathered and emitted in the same direction.

Although the light flux emitted from the single light source is firstsplit into two components so as to have the same polarization, and then,the split light fluxes are collected by the light gathering element, asin the illustrated embodiment, the present invention is not limitedthereto. For instance, the present invention can be applied to a lightgathering apparatus to gather two or more light fluxes having randompolarizations emitted from their respective separate light sources.

FIG. 9 shows a third embodiment of the present invention in which thelight source 10, collimating lens 11, polarization beam splitter 12, λ/2plate 13 and mirror 14 are replaced by two lamps A and B which emitlight fluxes of random polarization. The remaining construction is thesame as in the first embodiment (see FIG. 1). In this embodiment, thelight flux incident from lamp A is immediately reflected by the lightgathering mirror 30, whereas the light flux incident from lamp B isreflected first by mirror 15 and subsequently by light gathering mirror30.

I claim:
 1. A light gathering apparatus comprising:means for generatingat least two fluxes of light, said at least two fluxes of lightextending in different directions; and means for receiving andrefracting said at least two fluxes of light in order to form a combinedparallel light flux comprising said at least two fluxes of light, afterchanging the directions of said at least two fluxes of light so thatsaid at least two fluxes of light extend in the same direction, suchthat a uniform brightness is obtained, said means for receiving andrefracting comprising a flat incident surface upon which said at leasttwo fluxes of light are made incident, and an array of continuous firstand second emission surfaces which are alternately and symmetricallyarranged with respect to a bisection of an angle defined by and betweensaid at least two fluxes of light; wherein said means for receiving andrefracting substantially prevents vignetting in said combined parallellight flux by satisfying the following formulae:

    θ1=90°-2α;

    θ2=90°-α; and

    cos α={1+ 1+8(n.sub.1 /n.sub.2).sup.2 !.sup.1/2 }/{4·n.sub.1 /n.sub.2 };

wherein 2α equals an angle defining an intersection between each of saidfirst and second emission surfaces; wherein θ1 defines an angle ofincidence, of each of said at least two fluxes of light extending indifferent directions, on each of said first and second emissionsurfaces; wherein θ2 defines an angle of refraction at each of saidfirst and second emission surfaces; wherein n₁ defines a refractiveindex of said means for receiving and refracting; and wherein n₂ definesa refractive index of a medium at said emission surfaces of said meansfor receiving and refracting.
 2. A light gathering apparatus accordingto claim 1, wherein said at least two fluxes of light, upon beingrefracted by said means for receiving and refracting to form saidcombined parallel light flux, have a same polarization.
 3. A lightgathering apparatus according to claim 2, wherein said means forgenerating at least two fluxes of light comprises a polarization beamsplitter onto which a collimated light flux is incident from a lightsource; a λ/2 plate through which the light flux, having passed throughsaid polarization beam splitter, is transmitted; and reflection mirrorswhich reflect the light flux reflected by said polarization beamsplitter;wherein the light flux passed through said polarization beamsplitter and the light flux reflected by the mirrors comprise said atleast two fluxes of light and extend in different directions.
 4. A lightgathering apparatus according to claim 1, wherein said means forreceiving and refracting comprises a plurality of triangular posts, eachhaving said first and second emission surfaces, wherein each of saidtriangular posts comprises an apex defined by a pair of said first andsecond emission surfaces, and wherein each said apex is defined by anangle equal to 2α.
 5. A light gathering apparatus according to claim 1,wherein said at least two fluxes of light are made incident upon saidfirst and second emission surfaces at an incident angle of substantially60 degrees with respect to said bisection of an angle.
 6. A lightgathering apparatus according to claim 1, wherein said means forgenerating said at least two fluxes of light, generate light fluxes ofthe same polarization.
 7. A light gathering apparatus according to claim1, wherein said means for generating:diverts at least one of said atleast two fluxes of light to form said at least two fluxes of lightwhich extend in different directions.
 8. A light gathering apparatusaccording to claim 7, wherein said means for generating at least twofluxes of light comprises a mirror which reflects one of said at leasttwo fluxes of light.
 9. A light gathering apparatus according to claim1, wherein each of said at least two fluxes of light comprises a flux oflight which is parallel.
 10. A light gathering apparatuscomprising:means for generating at least two fluxes of light, said atleast two fluxes of light extending in different directions; and meansfor receiving and refracting said at least two fluxes of light in orderto form a combined parallel light flux comprising said at least twofluxes of light, after changing the directions of said at least twofluxes of light so that said at least two fluxes of light extend in thesame direction, such that a uniform brightness is obtained, said meansfor receiving and refracting comprising a flat incident surface uponwhich said at least two fluxes of light are made incident, and an arrayof continuous first and second emission surfaces which are alternatelyand symmetrically arranged with respect to a bisection of an angledefined by and between said at least two fluxes of light, wherein saidmeans for generating at least two fluxes of comprises a polarizationbeam splitter onto which a collimated light flux is incident from alight source; a λ/2 plate through which the light flux, having passedthrough said polarization beam splitter, is transmitted; and reflectionmirrors which reflect the light flux reflected by said polarization beamsplitter; wherein the light flux passed through said polarization beamsplitter and the light flux reflected by the mirrors comprise said atleast two fluxes of light and extend in different directions; whereinsaid means for receiving and refracting substantially preventsvignetting in said combined parallel light flux by satisfying thefollowing formulae:

    θ1=90°-2α; and

    θ2=90°-α;

wherein 2α equals an angle defining an intersection between each of saidfirst and second emission surfaces; wherein θ1 defines an angle ofincidence, of each of said at least two fluxes of light extending indifferent directions, on each of said first and second emissionsurfaces; and wherein θ2 defines an angle of refraction at each of saidfirst and second emission surfaces.
 11. A light gathering apparatusaccording to claim 10, wherein said at least two fluxes of light, uponbeing refracted by said means for receiving and refracting to form saidcombined parallel light flux, have a same polarization.
 12. A lightgathering apparatus according to claim 10, wherein said means forreceiving and refracting comprises a plurality of triangular posts, eachhaving said first and second emission surfaces.
 13. A light gatheringapparatus according to claim 12, wherein said plurality of triangularposts each have said first and second emission surfaces, wherein each ofsaid triangular posts comprises an apex defined by a pair of said firstand second emission surfaces, and wherein each said apex is defined byan angle equal to 2α.
 14. A light gathering apparatus according to claim10, wherein said at least two fluxes of light are made incident uponsaid first and second emission surfaces at an incident angle ofsubstantially 60 degrees with respect to said bisector of an angle. 15.A light gathering apparatus according to claim 10, wherein said meansfor generating said at least two fluxes of light, generate light fluxesof the same polarization.
 16. A light gathering apparatus according toclaim 10, wherein each of said at least two fluxes of light comprises aflux of light which is parallel.